Distribution and diversity of dimetal-carboxylate halogenases in cyanobacteria
Halogenation is a recurring feature in natural products, especially those from marine organisms. The selectivity with which halogenating enzymes act on their substrates renders halogenases interesting targets for biocatalyst development. Recently, CylC - the first predicted dimetal-carboxylate halogenase to be characterized - was shown to regio- and stereoselectively install a chlorine atom onto an unactivated carbon center during cylindrocyclophane biosynthesis. Homologs of CylC are also found in other characterized cyanobacterial secondary metabolite biosynthetic gene clusters. Due to its novelty in biological catalysis, selectivity and ability to perform C-H activation, this halogenase class is of considerable fundamental and applied interest. However, little is known regarding the diversity and distribution of these enzymes in bacteria. In this study, we used both genome mining and PCR-based screening to explore the genetic diversity and distribution of CylC homologs. While we found non-cyanobacterial homologs of these enzymes to be rare, we identified a large number of genes encoding CylC-like enzymes in publicly available cyanobacterial genomes and in our in-house culture collection of cyanobacteria. Genes encoding CylC homologs are widely distributed throughout the cyanobacterial tree of life, within biosynthetic gene clusters of distinct architectures. Their genomic contexts feature a variety of biosynthetic partners, including fatty-acid activation enzymes, type I or type III polyketide synthases, dialkylresorcinol-generating enzymes, monooxygenases or Rieske proteins. Our study also reveals that dimetal-carboxylate halogenases are among the most abundant types of halogenating enzymes in the phylum Cyanobacteria. This work will help to guide the search for new halogenating biocatalysts and natural product scaffolds. Data statementAll supporting data and methods have been provided within the article or through a Supplementary Material file, which includes 14 supplementary figures and 4 supplementary tables.